Removal of manganese from pulp fibers with MgS[O.sub.4] in a displacement system.

Application: This research suggests an effective method to remove manganese from pulp fibers.

Removal of manganese from pulp fibers is usually achieved in a chelation stage with DTPA or EDTA. It can also be carried out in a treatment with magnesium sulfate via the so-called ion exchange technique. In such a process, manganese, the "bad" metal ion present in pulp fibers, is replaced by magnesium, a "good" metal ion. If this ion exchange technique is conducted in a stirred tank reactor, a very high dosage of the good metal ions is required to decrease the manganese content to a reasonably low level. In this paper we report that the magnesium sulfate charge can be significantly decreased to have a good chelation result when the ion exchange technique is conducted in a displacement system. For example, with a magnesium sulfate charge of 1%, a residual manganese content of about 5 ppm can be reached from a pulp containing 150 ppm manganese. The manganese removal in such a process is similar to that during a conventional chelation stage with UFPA or EDTA. The bleaching responses in a subsequent peroxide stage of chelated pulps were compared.

Since the ion exchange process takes place so fast, process parameters, such as superficial velocity, temperature and residence time, have negligible effect on the overall performance. Due to the efficient removal of manganese of the resulting pulp by the ion exchange process in a displacement system, the subsequent bleaching in a peroxide stage yields comparable results as those from DTPA chelated pulp.

Li is a process engineer at Irving Paper Inc., P.O. Box 1900, Bayside Drive, Saint John, New Brunswick, Canada; Ni is a professor, Limerick Pulp and Paper Centre, University of New Brunswick, Fredericton, New Brunswick, Canada; van Heiningen is a professor, Department of Chemical Engineering, University of Maine, Orono, Maine, USA. Address correspondence to Ni by email at [e-mail].